High speed data connections that operate over wiring where other active connections are also operating in adjacent wiring may introduce interference, also known as cross-talk interference, into the adjacent wiring. This cross-talk interference can impact the quality of connections existing over the adjacent wiring reducing the distance over which the connection can operate and/or increasing the incidence of data errors over such connections.
FIG. 1 illustrates a conventional telecommunication system. Remote network elements 102 communicate with a central network element 104, such as a hub, switch, router or access multiplexer, over wired communications links 106 of varying lengths. A remote network element 102 may be a modem, a network interface device, a digital subscriber line (DSL), a router, and the like. Communication links 106 are subject to cross-talk interference from signals active over adjacent communication links coupled from remote network elements 102 to central network element 104. Other sources of noise or interference include transient signals resulting from electromagnetic signals created by other devices including motors, lights, radios, or other devices. Noise and interfering signals from a variety of sources combine to produce complex signals at each end of the communications links, at remote network elements 102 and central network element 104. These complex signals combine with the desired signals transmitted over communications links 106. The remote and central network elements 102 and 104 must be able to recover the desired signal in the presence of this interference. In addition, the strength of the desired signals and the interfering signals is affected by the attenuation of communications links 106. The amount of coupling between the communications links 106 also depends on parameters including the length, the degree of adjacency (closeness) over variable distances and the electrical characteristics of the communications links.106.
A variety of methods have been proposed for minimizing the level of interference in adjacent wiring. An example of such methods is a known power back-off technique used to control the uplink power level in DSL transmissions. Such power back-off techniques attempt to select an appropriate power level for the remote terminal transmitter power. Algorithms used to implement such techniques typically attempt to characterize the quality of the connection based on an analysis of the signal level received from the central network element equipment located at the origin of the connection.
For example, a central network element supporting more than one data connection, for example 10 connections, may use the power back-off algorithm to minimize the level of interference. Each of the 10 remote terminal devices will analyze the power level received from the central network element independently and will select a transmission power level. Because of differences in attenuation at different frequencies (for example, the transmission from the remote terminal device to the central network element may be at a different frequency) the remote terminal devices will in some instances select a transmission power level that is sub-optimal in reference to the ideal power level that would maximize the performance of all data connections to the central network element.
The sub-optimal results could include reduced signal quality on adjacent data connections due to some remote terminal devices transmitting at greater power levels than required. Another result could include remote terminals transmitting with a lower power level than the level that would maximize reliability of all data connections to the central network element device.
Algorithms that operate in the manner described above do not select optimal power levels for data connections that are operating in the middle of the dynamic range of the connection. These algorithms tend to select transmit power levels that are too low to optimize the performance over the data connections operating in the middle of the service range for the selected connection method by selecting the minimum required power to establish the connection. In addition, the independent calculation of power levels by each remote terminal may create a sub-optimal balance of signal levels at the central network element. Furthermore, the introduction of additional loss onto the data connection, particularly loss that is dependent on frequency, may cause the remote terminal to select power levels that further impact the performance of adjacent connections.
A need therefore exists for a method for optimizing the performance of a collection of multiple adjacent data connections by cooperatively selecting transmission power levels to meet specified performance criteria. In particular, the method should allow data connections operating on adjacent wiring connections to select mutually optimal transmitter power levels, therefore improving the performance of the overall communications system.